Android Question Directory Structure

On my Android device when connected via USB cable, I have created a folder "Books"
This directory now has the following folders:
Alarms
Android
DCIM
Download
google
Movies
Music
Notifications
Pictures
Podcast
Ringtones
Books

Within the "Books" folder, I have a number of PDF files that I wish to load.
What is the correct path syntax to be able to reach these PDF files?